The present invention relates to a cylinder lock with a body, in which a plug with a profiled, axially extending key slot is rotatably arranged, and in which the body and the plug are provided with a number of bores approximately perpendicular to the axis of the plug, in which bores a number of locking pins is provided, said locking pins comprising tumbler pins and driver pins, and in which the locking pins are lifted by insertion of a key such that the end faces of the tumbler pins flush with the circumferential surface of the plug, in which at least one of the driver pins comprises two members, of which a first member is movable relative to the second one in the longitudinal direction of the pins.
Locks of this type are commonly known and have a reputation of being reliable and offer the possibility of a large number of locking combinations without the locks becoming mechanically complicated. A drawback in the locks is that in case of the most widely known type with five or six locking pins, it is possible to open the locks with a comparatively simple equipment. The picking of the lock is performed by insertion in the key slot of an instrument which is arranged to act on all locking pins with an upwards stroke. By the impact the locking pins are influenced by a force which is transmitted through the tumbler pins to the driver pins which are then lifted free of the plug. It then becomes possible, in the short moment, in which the driver pins are lifted free of the plug, to rotate the plug, the lock thereby becoming open. Several arrangements have been proposed for the manufacture of locks, in which such a picking is not possible. Locks have for instance been manufactured, in which, in addition to the profiling on the upper edge of the key, a profiled groove is provided on one side of the key. The additional groove makes the lock more complicated and makes, in particular, the manufacture of additional copies of a certain key complicated and costly.
EP patent application No. 0 452 297 discloses a lock of the type mentioned by way of introduction, in which the spring-loaded driver pin is designed with a stepped portion extending in the direction towards the plug and is provided with a bush member displaceable relative to the driver pin. When the locking pins are affected by an impact, the driver pin moves, whereas the bush member, which is placed with its end face facing the plug at a distance from the tumbler pin, according to this publication will remain in substantially the same position and block any movement of the plug. Even though this arrangement, at least in theory, provides the effect aimed at, it is a requirement that the lock cylinder is positioned in such a manner that the locking pins extend downwards relative to the plug to move the bushing member in a position of rest downwards by gravitation to ensure a correct functioning. This orientation is, however, disadvantageous as it becomes easier in this way to pick the lock.
The object of the present invention is to provide a cylinder lock which offers a very high security against picking, and in which this effect can be attained, also in case of simply built locks with only five or six locking pins.
This object is met by means of a cylinder lock of the type mentioned by way of introduction, the lock according to the invention being characterized by the subject matter of the characterizing clause of claim 1.
The invention resides in the realization that the picking of cylinder locks is based on a dynamic effect. The stroke towards the tumbler pin is transmitted to the driver pin which is thereby lifted without any actual movement of the tumbler pin. By the arrangement according to the invention the effect of the impact is transmitted to the movable member which constitutes one part of the driver pin. The second member of the driver pin remains approximately stationary and therefore remains in the parting surface between plug and body, the result being that the plug cannot be rotated. If only one of the locking pins of the cylinder lock is designed as comprising two members, the desired pick-proof effect is attained, but if desired, several of the driver pins may consist of two members without making the lock substantially more costly. Hereby, an additional security is obtained against the pick-proof effect not being hampered on account of failure to maintain the lock.
Particular embodiments of the invention will appear from the dependent claims.